A can do a work in 21 days and B alone can…

A can do a work in 21 days and B alone can do it 28 days, they begin the work together, but A left after some days. B completed the remaining work in 21 days. After how many days did A leave ?

AQuA-RAT — Algebra Question Answering with Rationales (Ling et al., DeepMind, 2017) · train #50527